The purpose of this proposal is the investigation of a dopamine based mechanism for binge eating disorder. We propose to evaluate the effect of central dopamine manipulation (using methylphenidate, a drug that increases brain dopamine signaling) on binge eating behavior in obese women measured by food reinforced operant task performance. Binge eating behavior in obese individuals is believed to contribute to poor outcomes of weight loss and weight maintenance treatment. The underlying neurophysiology of binge eating in obese is still unknown. One potential modulator of binge eating is the neurotransmitter dopamine. Food intake and the willingness to "work" to acquire food (a surrogate measure of binge potential for a substance) both involve release of central dopamine. Leddy et al (2004) demonstrated that methylphenidate reduced food intake in a laboratory test meal in a small sample of obese men, no indication of the binge eating status of the men in the study was provided. We propose to extend these findings to women who have Binge Eating Disorder using an innovative and unique laboratory model of human binge eating. This model entails the consumption of 600 kcal of a mixed macronutrient liquid meal (50% CHO, 30% FAT, 20% PRO) followed 20 minutes later by performance of a food-reinforced operant task. The greater the binge eating tendency, the greater the number of food choices made in the operant task under placebo condition. We expect methylphenidate to reduce the number of food choices made in the operant task. We will test two active doses of methylphenidate and a placebo, all administered orally, on separate days, one hour before operant task performance. Relevance to Public Health: Data from this study should provide new insight into the relationship between brain dopamine and binge eating in obese women. Demonstration of a role for dopamine in binge eating provides an additional target for intervention.